The present invention relates to implantable electrode arrays, and more particularly to an implantable electrode array configured for implantation under the soft tissue or spiral ligament on the lateral wall of a human cochlea. Such electrode array is best suited for use with a hybrid cochlear stimulator of the type described in applicant""s international patent application, filed May 12, 2000, as Serial No. PCT/US00/13122, and published as International Publication WO 00/69512 on Nov. 23, 2000, entitled xe2x80x9cHybrid Implantable Cochlear Stimulation Hearing Aid Systemxe2x80x9d, which publication is incorporated herein by reference. In general, a hybrid cochlear stimulation system provides electrical stimulation only to the basal end of the cochlea to stimulate nerves, e.g., ganglion cells, hair cells, or other nerve cells, responsible for sensing higher-frequency sounds, and relies on normal hearing processes (activation of hair cells through fluid motion within the cochlea), which may occur with or without the assistance of a conventional or a custom hearing aid, to sense middle-to-lower frequency sounds.
Hearing loss is generally of two types: conductive and sensorineural. Of these, conductive hearing loss occurs where the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded, for example, by damage to the ossicles. Conductive hearing loss may often be helped by use of conventional hearing aids, which amplify sound so that acoustic information does reach the cochlea and the hair cells. Some types of conductive hearing loss are also amenable to alleviation by surgical procedures.
Sensorineural hearing loss, on the other hand, results due to the absence or the destruction of the hair cells in the cochlea which are needed to transduce acoustic signals into auditory nerve impulses. Persons who suffer from sensorineural hearing loss are unable to derive any benefit from conventional hearing aid systems, no matter how loud the acoustic stimulus is made, because their mechanisms for transducing sound energy into auditory nerve impulses have been damaged. Thus, in the absence of properly functioning hair cells, there is no way auditory nerve impulses can be generated directly from sounds.
To overcome sensorineural deafness, there have been developed numerous cochlear implant systemsxe2x80x94or cochlear prosthesisxe2x80x94which seek to bypass the hair cells in the cochlea by presenting electrical stimuli directly to the ganglia of the auditory nerve located adjacent the modiolar wall of the cochlea. When triggered, the ganglia, also referred to as ganglion cells, send nerve impulses to the brain via the auditory nerve, leading to the perception of sound in the brain, and an at least partial restoration of hearing function. The common denominator in such cochlear prosthesis systems has been the implantation into the cochlea of electrodes which are responsive to a suitable external source of electrical stimuli and which are intended to transmit those stimuli to the ganglion cells, and thereby to the auditory nerve fibers.
It is estimated that a large segment of the hearing-impaired population exhibit sensorineural hearing loss relative to high frequency sounds, but maintain the ability to transduce middle-to-lower frequency sounds through functioning hair cells. For this segment of the population, there is thus a need for a xe2x80x9chybridxe2x80x9d cochlear stimulation system that electrically stimulates only the cells and nerves responsible for sensing higher frequency sounds, while allowing the normal hearing process to function for the purpose of sensing lower frequency sounds.
A cochlear prosthesis operates by direct electrical stimulation of the auditory nerve cells, bypassing the defective cochlear hair cells that normally transduce acoustic energy into electrical activity in such nerve cells. Because the ganglion or other cells, e.g., hair cells, responsible for sensing higher frequency sounds are all generally located in or near the basal end of the cochlea (the end of the cochlea nearest the round window membrane), a hybrid cochlear stimulation system thus requires an electrode array that can be inserted within the cochlea a sufficient depth to be near such cells, but which also does not block or significantly interfere with the normal functioning of the cochlea for hair cells located deeper within the cochlea. A preferred electrode array for use with such a hybrid cochlear stimulation system would be inserted into or near the cochlea in such a way so as not to interfere with the normal functioning of the cochlea. No such electrode array, to applicants"" knowledge, currently exists.
The present invention addresses the above and other needs by providing a cochlear electrode array suitable for use with a hybrid cochlear stimulation system. In one embodiment, the cochlear electrode array comprises a relatively thin blade electrode array that is inserted underneath the spiral ligament, or soft tissue, at the lateral wall of the cochlea, without actually penetrating into any of the three main ducts that make up the cochlea: the scala tympani, the scala vestibule, or the cochlear duct.
In accordance with one aspect of the invention, the blade electrode provided by the invention is implanted into the cochlea through a xe2x80x9csoft cochleostomyxe2x80x9d operation. A soft cochleostomy operation is one wherein a hole is drilled into but not all the way through the bony tissue adjacent the round window. Hence, no penetration occurs into the cochlea ducts, including the scala tympani, the scala vestibule, and the cochlear duct, and all such ducts remain intact to perform their normal function.
Once a soft cochleostomy hole has been drilled, the blade of a suitable surgical instrument, or a similar tool, is inserted into the drilled hole and is used to delaminate the spiral ligament membrane from the bony tissue located at the lateral wall of the cochlea. The blade electrode of the invention is then slid into the opening created by the tissue delamination to a desired depth. The desired depth will typically be a relatively short distance, e.g., 6-12 mm. However, for some applications, the blade electrode may be inserted sufficiently deep so as to make up to a 180xc2x0 turn through the cochlea.
In accordance with another aspect of the invention, the blade electrode array incorporates thin lips or side fins that extend beyond the body of the carrier of the electrode itself. Such side fins are used to fix the electrode in a groove in the bony recess prepared to hold the electrode.
In accordance with yet an additional aspect of the invention, used in an alternative embodiment thereof, the blade electrode carries one or more mechanical transducers that convert electrical current to mechanical energy, which mechanical energy is then readily coupled directly to the fluid within the cochlea, thereby assisting or aiding the triggering of hair cells that line the inside of the cochlea.
In accordance with yet another aspect of the invention, the blade electrode is inserted under the spiral ligament membrane at the lateral wall of the cochlea and is selectively energized in order to treat tinnitus.
It is a feature of the present invention to provide an electrode array for stimulating nerves and cells of the inner ear, e.g., the cochlea, without interfering with the normal operation of the inner ear, thereby allowing the selective activation of such electrode array to supplement the normal hearing processes that occur within the inner ear.
It is another feature of the invention to provide a method of inserting an electrode array into the inner ear without penetrating into the scala tympani or scala vestibuli of the cochlea, thereby permitting the cochlea to perform its normal hearing function in a minimally-invasive manner.